Fuel injection valve

ABSTRACT

The invention relates to a fuel injection valve for injecting fuel into a combustion chamber of an internal combustion engine, having a nozzle needle ( 1 ) which is guided, such that it can perform a stroke movement, in a central bore ( 2 ) of a nozzle body ( 3 ) in order to open up or close off at least one injection opening ( 4 ), wherein the nozzle needle ( 1 ) interacts, by means of an encircling sealing region ( 5 ) formed on the combustion-chamber-side end thereof, with a sealing seat ( 6 ) that runs conically and is formed on the combustion-chamber-side end of the nozzle body ( 3 ). According to the invention, the sealing seat ( 6 ) that runs conically has an opening angle (α 1 ) of between 30° and 50°, preferably of between 40° and 50°.

BACKGROUND OF THE INVENTION

The invention relates to a fuel injection valve for injecting fuel intoa combustion chamber of an internal combustion engine.

German Laid-Open Application DE 10 2006 012 242 A1 has disclosed a fuelinjection valve for an internal combustion engine, which has a valvebody, in which there is formed a pressure space which can be filled withfuel at high pressure and from which at least one injection openingstarts. Arranged in the pressure space is a longitudinally movable valveneedle, which interacts by means of a sealing surface with a conicalvalve seat formed in the pressure space in order to open and close theat least one injection opening. To ensure that sufficient fuel flowsbetween the sealing surface of the valve needle and the valve seat tothe injection openings to achieve an appropriate injection rate, thevalve needle must traverse a certain minimum stroke. This is because itis first necessary to cross the region in which the gap between thesealing surface and the valve seat exerts a restricting effect and theinjection pressure prevailing at the injection openings is reduced. Witha large minimum stroke for achieving the full injection pressure,however, it is not possible to achieve a rapid succession of injections.In the laid-open application mentioned above, therefore, a conicallyformed valve seat with an opening angle of between 75° and 100° isproposed. Compared with fuel injection valves which have a conical valveseat with a conventional opening angle of about 60°, the fuel injectionvalve proposed has the advantage that the stroke of the valve needlerequired to traverse the seat restriction region is smaller and, as aresult, a rapid succession of injections at a high injection pressure ispossible. Moreover, the larger opening angle of the valve seat issupposed to reduce flow-induced disturbing forces on the valve needle,which can cause axial misalignment of the valve needle.

Given the constant increase in injection pressures, strengthconsiderations, especially in the region of the valve seat, are nowadaysto the fore in the development of modern fuel injection valves. In thiscontext, the seat geometry chosen has a major influence on the operationof the fuel injector.

It is therefore the object of the present invention to provide a fuelinjector which has a high strength, especially in the region of thevalve seat.

SUMMARY OF THE INVENTION

The fuel injection valve proposed in order to achieve the object has anozzle needle which is guided, such that it can perform a stroke motion,in a central bore of a nozzle body in order to open or close at leastone injection opening, wherein the nozzle needle interacts, by means ofan encircling sealing region formed on the combustion-chamber endthereof, with a conically extending sealing seat, which is formed on thecombustion-chamber end of the nozzle body. According to the invention,the conically extending sealing seat has an opening angle α₁ of between40° and 50°. The advantage of such a seat geometry is that significantstress reductions can be achieved in the region of the sealing seat atthe combustion-chamber end of the nozzle body owing to the smalleropening angle, which is well below the customary 60°. Owing to thestress reduction achieved or the lower loads imposed, it is possible,for example, to increase the injection pressure by corresponding values.As an alternative or as a supplementary measure, it is also possible forthe nozzle body to have a smaller wall thickness in the region of theinjection openings, with the result that the injection openings have ashorter length, and this, in turn, has a favorable effect onsusceptibility to coking. Although it is also possible to achieve ahigher strength or greater robustness of the sealing seat region bytaking other strength-increasing measures, such as a higher grade ofmaterial, thicker walls or reinforcements, these measures are generallymore costly and, as a rule, do not fail to affect the operation of thefuel injector.

Since there is the risk of axial misalignment of the nozzle needle,provision is furthermore made to form a guiding region, close to theseat, in the central bore for guiding the nozzle needle. The term “closeto the seat” is used in the present case to refer to a guiding regionwhich is formed within a region of the central bore, the length of whichis no more than 40% of the total length of the nozzle body, startingfrom the combustion-chamber end of the nozzle body. By means of guidanceclose to the seat, axial misalignment or skewing of the nozzle needlecan be counteracted.

Good jet symmetry and hence uniform distribution of the injected fuel inthe combustion chamber of the internal combustion engine is thusensured, something that would otherwise not be assured, especially inthe case of valve-covered orifice nozzles, owing to the possible axialmisalignment of the nozzle needle. For this purpose, the central borehas a region of reduced diameter for the formation of the guiding regionclose to the seat.

The seat geometry proposed entails a larger nozzle needle stroke toeliminate the restriction at the seat. Accordingly, quick-acting valvesare preferably used in the fuel injection valve proposed. These make itpossible for the stroke region above the seat restriction to be reachedmore quickly, thus ensuring that the full injection pressure isavailable at the injection openings within a short time. In order toincrease the rapidity of the nozzle needle, a large ratio of thedischarge to the feed restrictor can be chosen, for example. Thus largerneedle strokes are compensated for by a “quick” needle. On the otherhand, small and very small injection quantities can be metered moreaccurately through deliberate exploitation of the nozzle restrictionregion and of a reduced needle force in the case of small needlestrokes. This is because a fuel injection valve according to theinvention has a smaller needle force in the case of small needle strokescompared with fuel injection valves that have a 60° valve seat openingangle. This furthermore has the effect that when a servo valve is usedfor control of the nozzle needle, the control space is relieved morequickly, with the result, in turn, that the nozzle needle undergoes anacceleration.

According to a preferred embodiment, the at least one injection openingopens into the central bore of the nozzle body in the region of thesealing seat. Accordingly, the fuel injection valve preferably has whatis referred to as a valve-covered orifice nozzle. Compared withblind-hole nozzles, in which the injection openings open into a blindhole below the sealing seat, valve-covered orifice nozzles have theadvantage inter alia that the dead volume can be reduced by up to 50%.Owing to the smaller dead volume, hydrocarbon emissions are alsosignificantly reduced. Since requirements as regards emissions are alsoconstantly rising, reducing these emissions can be seen as a furtherobject of the present invention. Thus, the proposed seat geometry for afuel injection valve according to the invention, combined with design asa valve-covered orifice nozzle, proves particularly advantageous. Owingto the injection openings formed in the seat region, a valve-coveredorifice nozzle does generally have a lower strength than a blind-holenozzle but this is compensated for by the fact that it is possible tosignificantly reduce stresses through the proposed smaller opening angleof the sealing seat.

The guiding region close to the seat is preferably formed immediatelyadjacent to the sealing seat. On the one hand, this makes it possible toachieve optimum guidance of the nozzle needle and, on the other hand,the production of the guiding region within the central bore issimplified. The central bore has a reduced diameter to form the guidingregion, and hence a region of the central bore with a larger diameteradjoins just one end of the guiding region, namely the end remote fromthe seat, making it possible to produce this enlarged diameter in asimple manner by opening it up.

The encircling sealing region formed on the nozzle needle preferably hasat least one conical partial region. The cone angle α₂ of this partialregion is preferably at least slightly larger than the opening angle α₁of the sealing seat. The nozzle needle thus essentially rests againstthe sealing seat with a linear sealing contour. To form a sealing edge,the encircling sealing region can also be composed of two conicalpartial regions with different cone angles.

According to a preferred embodiment, the encircling sealing regionformed on the nozzle needle has a pressure step with hydraulic effectivesurfaces which can be subjected to fuel pressure in an axial and/or aradial direction. Such a pressure step can also take the form of anencircling groove, for example. A hydraulic pressure applied thereto andacting in a radial direction can likewise contribute to guidance of thenozzle needle and thus prevent the risk of axial misalignment.

By virtue of the abovementioned characteristics, a fuel injection valveaccording to the invention is suitable particularly for moderncombustion methods involving a high proportion of premixed combustion inthe part-load range, which produce significantly increased hydrocarbonemissions. The nozzle designs which are usually chosen contribute to theincreased emissions. This is because the injection nozzle is generallydesigned as a blind-hole nozzle with a seat cone angle of about 60°. Incontrast, the nozzle design proposed here is capable of significantlyreducing hydrocarbon emissions, of ensuring good spray symmetry and ofachieving a strength in the nozzle region which allows high injectionpressures. Moreover, the ballistic fuel injection valves without astroke stop are widely used. A fuel injection valve according to theinvention can also be designed in this way.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail below with reference to thefigures, of which:

FIG. 1 shows schematic partial sections in the region of the sealingseat, contrasting a 45° nozzle according to the invention with a known60° nozzle, and

FIG. 2 shows schematic partial sections, contrasting a valve-coveredorifice nozzle with a blind-hole nozzle.

DETAILED DESCRIPTION

Of the comparative views in FIG. 1, that on the left shows a nozzledesign according to the invention and that on the right shows a knownnozzle design. Both nozzle designs comprise a nozzle needle 1 which isguided, such that it can perform a stroke motion, in a central bore 2 ofa nozzle body 3. For this purpose, the nozzle design according to theinvention has a guiding region 7 of reduced diameter close to the seat.The stroke motion of the nozzle needle 1 is used to open or close atleast one injection opening 4. Both nozzles are designed asvalve-covered orifice nozzles, that is to say the at least one injectionopening 4 in each case opens into the central bore 2 in the region of asealing seat 6 formed within the central bore 2. In each case, thesealing seat 6 has a conical shape which corresponds substantially to aconically extending partial region 8 of the nozzle needle 1 and forms asealing region 5. Adjoining the conical partial region 8 of the nozzleneedle 1 is a cylindrical partial region, followed in turn by a conicalpartial region, thus forming a pressure step 9 on the nozzle needle 1and an annular space as a pressure chamber between the nozzle needle 1and the sealing seat 6, this space being filled with fuel at highpressure during the operation of the injection valve. The pressurechamber is connected to an annular gap formed between the nozzle needle1 and the central bore 2, said gap likewise serving as a pressure space.At the combustion-chamber end (at the bottom in FIG. 1), the centralbore 2 in each case ends in a blind hole 10. The only differences areessentially those in respect of the chosen opening angle α₁ of theconically extending sealing seat 6, which is 45° in the left-hand imageand 60° in the right-hand image, and the cone angle α₂ of the conicalpartial region 8 of the nozzle needle 1, which is of correspondingconfiguration in each case.

FIG. 2 shows a valve-covered orifice nozzle (left-hand side) and ablind-hole nozzle (right-hand side) in comparison. In the case of thevalve-covered orifice nozzle, the at least one injection opening 4 opensinto the central bore 2 of the nozzle body in the region of the sealingseat 6, while, in the case of the blind-hole nozzle, the at least oneinjection opening 4 opens into the blind hole 10. In the case of thevalve-covered orifice nozzle too, a dead volume remains in the blindhole 10 when fuel is injected into the combustion chamber of an internalcombustion engine. As can be seen from the views in FIG. 2, however,this is significantly reduced, i.e. by about 50%. When using avalve-covered orifice nozzle, it is thus likewise possible significantlyto reduce hydrocarbon emissions, and this is a further advantage.

1-7. (canceled)
 8. A fuel injection valve for injecting fuel into acombustion chamber of an internal combustion engine, having a nozzleneedle (1) which is guided, such that the needle can perform a strokemotion, in a central bore (2) of a nozzle body (3) in order to open orclose at least one injection opening (4), wherein the nozzle needle (1)interacts, by means of an encircling sealing region (5) formed on acombustion-chamber end thereof, with a conically extending sealing seat(6), which is formed on a combustion-chamber end of the nozzle body (3),characterized in that the conically extending sealing seat (6) has anopening angle (α₁) of between 40° and 50°, and the central bore (2) hasa guiding region (7) of reduced diameter, close to the seat, for guidingthe nozzle needle (1), wherein the guiding region (7) is formed within aregion of the central bore (2), the length of which is no more than 40%of the total length of the nozzle body (3), starting from thecombustion-chamber end of the nozzle body (3).
 9. The fuel injectionvalve as claimed in claim 8, characterized in that the at least oneinjection opening (4) opens into the central bore (2) in the region ofthe sealing seat (6).
 10. The fuel injection valve as claimed in claim8, characterized in that the guiding region (7) close to the seat isformed immediately adjacent to the sealing seat (6).
 11. The fuelinjection valve as claimed in claim 8, characterized in that theencircling sealing region (5) formed on the nozzle needle (1) has atleast one conical partial region (8).
 12. The fuel injection valve asclaimed in claim 8, characterized in that the encircling sealing region(5) formed on the nozzle needle (1) has at least one conical partialregion (8), wherein a cone angle (α₂) of the partial region (8) is atleast slightly larger than the opening angle (α₁) of the sealing seat(6).
 13. The fuel injection valve as claimed in claim 8, characterizedin that the encircling sealing region (5) formed on the nozzle needle(1) has a pressure step (9) with hydraulic effective surfaces which canbe subjected to fuel pressure in an axial and/or a radial direction. 14.The fuel injection valve as claimed in claim 9, characterized in thatthe guiding region (7) close to the seat is formed immediately adjacentto the sealing seat (6).
 15. The fuel injection valve as claimed inclaim 14, characterized in that the encircling sealing region (5) formedon the nozzle needle (1) has at least one conical partial region (8).16. The fuel injection valve as claimed in claim 14, characterized inthat the encircling sealing region (5) formed on the nozzle needle (1)has at least one conical partial region (8), wherein a cone angle (α₂)of the partial region (8) is at least slightly larger than the openingangle (α₁) of the sealing seat (6).
 17. The fuel injection valve asclaimed in claim 16, characterized in that the encircling sealing region(5) formed on the nozzle needle (1) has a pressure step (9) withhydraulic effective surfaces which can be subjected to fuel pressure inan axial and/or a radial direction.